From U.S. Pat. No. 3,735,458 a double-layer rotary anode and a method for manufacturing such a double-layer rotary anode from a tungsten anode portion and a supporting portion of a cast molybdenum alloy is known.
As a molybdenum alloy for the supporting portion, a material known under the trade name “TZM” is used. Besides molybdenum, this material contains titanium, zirconium and carbon. It is satisfactory workable by temperature and deformation treatments already carried out in the metallurgical factory. The admixtures of titanium and zirconium in the molybdenum lower the melting point so that this material can be cast and the re-crystallization temperature is raised to 1,800° C. Thus the increase in mechanical strength achieved in this manufacture of the rotary anode is maintained even under heavy operational conditions, provided that the temperature of the supporting portion remains below 1,800° C.
According to U.S. Pat. No. 3,735,458, from a rod of this material a disc is formed and smoothed on at least one side by conventional cutting processes.
Further, a disc of tungsten forming the anode portion is manufactured, this disc being smoothed to the optimum at least on one side by grinding and/or polishing so that at the same time a clean surface free of an oxide skin is obtained.
The anode portion and supporting portion discs are then joined by their smooth sides and heated in an oven at a temperature of about 1,650° C. in a non-oxidizing or reducing atmosphere. After heating, the joined anode portion and supporting portion discs are conveyed as quickly as possible, in order to restrict any oxidation and to minimize cooling, to a quick-action impact forming device. In this device, the anode portion and supporting portion discs are pressed together with a high-energy stroke. Thereby, the two discs form an intimate bond at a very high pressure. Since the deformation takes place below the re-crystallization temperature of 1,800° C. of the supporting portion, so that a cold-state deformation is concerned here, the high deformation produced by the impact will provide in addition a high stiffening of the supporting portion.
However, in modern rotary anode X-ray tubes, the rotary anode is subjected to extreme thermal and mechanical loads during operation of the rotary anode X-ray tube. Such, the temperature of the anode disc at the anode portion, especially at a focal track where during operation an electron beam emitted by a cathode is hitting the anode portion, may be extremely high. This may have unwanted impacts on the material of the supporting portion of the anode disc, and especially may lead to unwanted changes of the material properties of the material of the supporting portion of the anode disc.